The China State Intellectual Property Office's (SIPO's) Patent Reexamination Board has declared invalid the patent for Viagra, the US pharmaceutical company Pfizer's treatment for erectile dysfunction. The board said the related documentation fails to conform to Article 26 of the Patent Law.

Sources at SIPO declined to provide further comment.

The law requires companies to provide a description of the drug "... in a manner sufficiently clear and complete so as to enable a person skilled in the relevant field to understand the drug. The abstract shall state the main technical points of the invention or utility model."

Pfizer said it will appeal the decision.

The active ingredient in Viagra is sildenafil, and the decision by SIPO's Patent Reexamination Board overturns the sildenafil-use patent issued in China in September 2001, the company said.

Pfizer said the patent remains in effect until a court resolves the issue, but Article 47 of the Patent Law states that any patent right that has been declared invalid is treated as non-existent.

Pfizer has three months in which to file its case in the people's court.

Viagra entered the Chinese market in July 2000. Many domestic companies opposed the patent because drugs produced by some Chinese companies were already using sildenafil in their products, Sina.com.cn news reported.

Granting the patent to Pfizer meant that until 2014, any domestic company using sildenafil citrate to produce drugs for the treatment of erectile dysfunction would be regarded as patent violators. In October 2001, 12 domestic pharmaceutical companies requested SIPO to cancel the patent rights.

(China Daily July 9, 2004)